(a) General Provisions. The following Design Criteria are summarized herein to establish practical, uniform design of sanitary sewers within the City. These criteria cover design factors and approved guidelines for evaluation of plans and specifications by the political subdivisions having jurisdiction over the review of plans and specifications. These design factors are consistent with the requirements of the OEPA. If these Design Criteria should conflict in the future with the requirements of the OEPA, these criteria shall be modified to conform to their requirements. These Design Criteria are also intended to conform to the City Standard Drawings for sanitary sewers.
(b) Basis of Design. The basis of design shall be the Manning Formula. This is used to calculate the capacity of a pipe flowing full:
Q= 1.486 R2/3 S1/2 A n |
Q = Flow in cfs
A = Area of cross section - square feet
n = Coefficient of roughness (n = 0.013)
R = Hydraulic Radius - feet
S = Slope in ft/ft
(c) Maximum Depth of Flow. Recommended design practices limit the depth of flow in a sanitary sewer. The maximum depth of flow should be equal to or less than 0.8 of the diameter of the pipe.
(d) Average Daily Flow. The average daily flow shall be 100 gallons per capita per day and includes normal infiltration.
(e) Population Density. The average household consists of 4 persons. Therefore, for design purposes, there would be 4 capita per equivalent single-family dwelling.
(f) Peak Design Flow. Sanitary sewers shall be designed on a peak design flow basis using one of the following methods:
(1) The ratio of peak average flow (ADF).
(2) Values established from the infiltration/inflow study approved by the OEPA.
(3) Values obtained from the flow records of a similar facility over a period of time sufficient to establish with a reasonable degree of reliability the relationship between average dry weather flow and peak design flow.
(4) Peak flows as determined by the Great Lakes Upper Mississippi River Board (GLUMRB) (Ten States Standards), latest version.
Use of other values for peak design flow will be considered, if justified, on the basis of extensive documentation.
SUGGESTED SEWAGE FLOW GUIDE
ESTIMATED SEWAGE FLOW (ADF)
WASTEWATER SOURCE | GALLONS PER DAY | LITERS PER DAY |
Airports | ||
Per Employee | 20 | 76 |
Per Passenger | 5 | 19 |
Apartments | ||
One Bedroom | 250 | 947 |
Two Bedrooms | 300 | 1,137 |
Three Bedrooms | 350 | 1,326 |
Assembly Halls | ||
Per Seat | 2 | 8 |
Bowling Alleys (no food service) | ||
Per Lane | 75 | 284 |
Camps | ||
Individual bath units - per units | 50 | 189 |
Central Bathhouse - per person | 35 | 133 |
Car Wash (per car, no recycling) | 80 | 304 |
Churches | ||
Small - per sanctuary seat | 3-5 | 11-19 |
Large with kitchen - per sanctuary seat | 5-7 | 19-27 |
Country Clubs (including food service) | ||
Per Member | 50 | 189 |
Dance Halls | ||
Per person | 2 | 9 |
Factories | ||
No showers - per employee | 25 | 95 |
With showers - per employee | 35 | 133 |
Family Dwellings | ||
Per person | 100 | 379 |
*Food Service Operations | ||
Ordinary Restaurant (not 24 hour) per seat | 35 | 133 |
24-hour Restaurant | 50 | 189 |
* The listed estimated sewage flows are to be used for the design of sewers and should not be used for the design of treatment units. | ||
Banquet rooms - per seat | 5 | 19 |
Restaurant along freeway - per seat | 100 | 379 |
Tavern (very little food servie) per seat | 35 | 133 |
Curb Service (drive in) - per car space | 50 | 189 |
Vending Machine Restaurants - per seat | 35 | 133 |
Highway Rest Areas | ||
Per Car | 1-9 | 4-34 |
Hospitals | ||
No resident personnel - per bed | 300 | 1,137 |
Institutions | ||
Residents - per bed | 100 | 379 |
Laundries | ||
Coin operated - per machine (standard size machine) | 400 | 1,137 |
Motels | ||
Per Unit | 100 | 379 |
Nursing and Rest Homes | ||
Per patient | 150 | 568 |
Per resident employee | 100 | 379 |
Office Buildings | ||
(exclusie of cafeteria or kitchen) Per employee per shift | 20 | 76 |
Parks | ||
With toilet facility per person | 5 | 19 |
With showers, bathhouse, toilets, - per person | 10 | 38 |
WASTEWATER SOURCE | GALLONS PER DAY | LITERS PER DAY |
Schools | ||
Elementary (not including showers or cafeteria) per pupil | 1- | 38 |
High and Junior High (not including showers or cafeteria) per pupil | 15 | 57 |
Add for cafeteria - per pupil | 5 | 19 |
Add for showers - per pupil | 5 | 19 |
Service Stations | ||
First bay | 1,000 | 3,789 |
Each additional bay | 500 | 1,895 |
Shopping Centers | ||
(without food service or laundries) per acre of floor space | 0.2 per sq. ft. | 8 per sq. meter |
Stores | ||
Per toilet per shift | 400 | 1,516 |
Swimming Pool | ||
(average with hot water shower) per swimmer (design load) | 3-5 | 11-19 |
Theaters | ||
Drive-in Movies - per car space | 5 | 19 |
Movie - per seat | 5 | 19 |
Trailer Parks | ||
Per Trailer space | 300 | 1,137 |
Travel Trailer Dumping Stations | ||
At service station | Consult District Office of OEPA | |
Travel Trailer Parks and Camps | ||
- Per trailer or tent space | 125 | 474 |
Vacation Cottage | ||
- Per peson | 50 | 189 |
Youth and Recreation Camps | ||
- Per person | 50 | 189 |
(g) Minimum Velocity. All sanitary sewers shall be designed to give a mean velocity of at least 2.0 feet per second, when flowing full, based on Manning’s Formula using an “n” value of 0.013. Use of other “n” values will be considered, if deemed justifiable, on the basis of extensive field data.
(h) Maximum Velocity. The maximum velocity shall be 15 feet per second. If the velocity is greater than 15 feet per second, provisions should be made to protect against displacement.
(i) Minimum Grades. All sanitary sewers shall be designed to give a mean velocity of at least 2.0 feet per second when flowing full based on Manning’s Formula. Values of “n” to be used with the Manning Formula vary from 0.010 to 0.015 with 0.013 recommended. Use of “n” values other than 0.013 may be considered, if justified. Use of formulas other than Manning’s Formula may be accepted. If plans are recommended for approval with a slope less than the minimum, the consulting Engineer must show justification for the recommendation and obtain approval from OEPA. See Table 9.1.
TABLE 9.1
REQUIRED MINIMUM SLOPE
Based on “n” Value of 0.013
Sewer Sizes - 8 through 36 inches
Sewer Size | Minimum Slope in Feet Per 100 Feet |
8 | 0.40 |
10 | 0.28 |
12 | 0.22 |
15 | 0.15 |
18 | 0.12 |
21 | 0.10 |
24 | 0.08 |
27 | 0.067 |
30 | 0.058 |
36 | 0.046 |
(j) Sanitary Sewers. In general, the minimum size of sanitary sewers shall be 8 inches. However, 6-inch sanitary sewers may be used as private lateral sewers for apartments, camps, schools, restaurants, and other semi-public operations, provided their hydraulic capacity is not exceeded because of short run-off periods (high peak flows).
The lateral connections shall be premium joint construction and should be made of the same material as the street sewer whenever possible to minimize infiltration from the connection between the street main and house lateral. When joint material and/or dimensions are not compatible, a commercial adapter shall be provided.
(k) House Laterals. Minimum of 4-inch sewer pipe may be used for house connections. The cover over the lateral coming out of the house shall be a minimum 3-foot depth. The house connections shall be of premium joint construction and made of PVC schedule 40 pipe or SDR 35. Cleanouts are required outside all structures or units and at property lines. In multi- tenant buildings, individual services shall be provided to a common pipe, then to the main. Individual water meters shall be used for separate sanitary sewers. When joint material and/or dimensions are not compatible, a commercial adapter shall be provided. A copy of an ordinance or regulation requiring this type of construction must be on file with OEPA district office or submitted with all sewer plans to receive approval.
(l) Invert Drop in Manhole. When a smaller sewer discharges into a larger one, the invert of the larger sewer should be lowered sufficiently to maintain the same energy gradient. An approximate method for securing this result is to place the 0.8 depth point of both sewers at the same elevation or matching the top elevation of the pipes. When a larger sewer discharges into a smaller, the invert of the smaller should not be raised to maintain the same energy gradient.
(m) Illegal Connections. Roof drains, foundation drains, sump pumps, yard drains, and all other clear water connections to the sanitary sewer are prohibited.
There shall be no physical connection between a public or private potable water supply system and a sewer or appurtenances thereto which would permit the passage of any sewage or polluted water into the potable supply.
(n) Horizontal Separation. If possible, sanitary sewers and sewage force mains should be laid with at least a 10-foot horizontal separation from any water main.
(o) Vertical Separation. Sewers (or sewage force main) may be laid closer than 10 feet to a water main if it is laid in a separate trench and elevation of the crown of the sewer (or sewer force main) is at least 18 inches below the bottom of the water main. If it is impossible to maintain the 18-inch vertical separation when the sewer is laid closer than 10 feet to the water main, the sanitary sewer should be constructed of (or encased in) water main type materials which will withstand a 50 psi water pressure test.
If a sewage force main is laid closer than 10 feet to a water main, in no case should the sewage force main be laid such that the crown of the sewage force main is less than 18 inches below the water main.
(p) Crossing Utilities. Whenever a sanitary sewer and water main must cross, the sewer shall be laid at such an elevation that the crown of the sewer is at least 18 inches below the bottom of the water main. If it is absolutely impossible to maintain the 18-inch vertical separation, the sanitary sewer should be constructed of (or encased in) water main type material which will withstand a 50-psi water pressure test for a distance of 10 feet on both sides of the water main.
Whenever a sewage force main and water main must cross, the sewage force main shall be at least 18 inches below the bottom of the water main.
(q) Parallel Installation. Sanitary sewers and manholes should be laid with at least 10 feet, measured from edge to edge, horizontal separation from any water main. If separation can not be maintained, the sanitary sewer shall be constructed to water main standards.
(r) Manholes. Manholes shall be installed at the end of each line; at all changes in grade, size, and alignment; and at all pipe intersections. Manholes shall be installed at a distance not greater than 400 feet. Greater spacing may be allowed in larger sewers and in those carrying a settled effluent.
Manholes may be either poured in place or pre-cast concrete. Concrete construction shall conform to ASTM C-478 with joints between sections conforming to ASTM C-443.
The flow channel through manholes should be made to conform in shape, slope, and smoothness to that of the sewers.
All manhole covers shall be adjusted to grade by the use of no more than 12 inches of pre- cast concrete adjusting collars. In areas outside the pavement, the manhole casting should be adjusted so that the top is slightly above grade to prevent the entrance of the surface water.
(s) Manhole Minimum Diameter. Manholes shall be constructed large enough to allow access to the sewer. The minimum diameter of manholes shall be 48 inches. Where manhole diameters of greater than 48 inches are used to accommodate the sewer pipes, the manhole shall be returned to 48-inch diameter as soon as practical above the sewer crown. Manhole openings 24 inches or larger are required for easier access with safety equipment to facilitate maintenance.
(t) Manhole Water Tightness. Manholes shall be constructed to permit casting adjustments by use of cast-in-place or pre-cast concrete adjusting collars not to exceed 12 inches in height. Solid manhole covers shall be used in all pavement locations. In other areas, the manhole casting shall be adjusted so the top of the manhole cover is slightly above grade to prevent the entrance of the surface water. In areas subject to flooding, secured watertight and solid manhole covers should be used. All manhole covers, seating frames, and adapter rings shall be machined to a firm and even bearing to provide a true fit into the frames. Manholes shall be installed with chimney seals and water tight dishes.
Inlet and outlet pipes should be joined to the manhole with a gasketed and/or flexible watertight connection meeting ASTM Specification C-443. Where three or more manholes in sequence are to be constructed with solid, watertight covers, adequate ventilation shall be provided.
(u) Flow Channel. The invert of the lowest pipe entering a manhole shall be at least 3 inches (75 mm) above the top of the base slab so that the sewer flow channel maybe installed and shaped when channel is not precast. The flow channel through the manholes should be made to conform in shape, slope, and smoothness to that of the sewers.
Cut pipe shall not extend beyond the inside face of the manhole wall. Concrete placed inside the manhole to form the channel through the manhole shall not be placed between the pipe and the opening so as to interfere in any way with the flexibility of the joint.
(v) Drop Manholes. Drop manholes shall be used when the invert of the inflow sewer is 2.0 feet or higher than the manhole invert. When this difference of elevation is less than 2.0 feet, the manhole invert shall be filled and channeled to prevent solids deposition.
Due to the unequal earth pressure that would result from the backfilling operation in the vicinity of the manhole, the entire outside drop connection shall be encased in concrete.
Drop manholes shall be constructed with outside drop connection, except where such connections are not practical. Inside drop connection to be used only with the approval of the City. Manholes located in isolated areas should be provided with bolted covers for safety and to discourage vandalism.
(w) Test Inspection. The leakage and deflection tests are to be carried out by the contractor and witnessed and certified by the City officials and/or their representative.
All pipe which does not meet the testing requirements must be repaired and retested until it meets the requirements.
(x) Railroad and Highway Crossings. When boring is required, the casing pipe shall be designed to meet the requirements of the authority having jurisdiction and in compliance with the City of Urbana Construction Standards and Drawings. The size of the casing pipe shall be at least 4 inches greater than the largest outside diameter of the sewer pipe, joints, or couplings.
(y) Stream Crossings.
(1) Location of sewers in streams.
A. Cover depth. The top of all sewers entering or crossing streams shall be at a sufficient depth below the natural bottom of the streambed to protect the sewer line. In general, the following cover requirements must be met:
1. One foot of cover where the sewer is located in rock.
2. Three feet of cover in other material. In major streams, more than 3 feet of cover may be required.
3. In paved stream channels, the top of the sewer line should be placed below the bottom of the channel pavement.
Less cover will be approved only if the proposed sewer crossing will not interfere with the future improvements to the stream channel. Reasons for requesting less cover shall be provided in the project proposal.
B. Horizontal Location. Sewers located along streams shall be located outside of the streambed and sufficiently removed therefrom to provide for future possible stream widening and to prevent pollution by siltation during construction.
C. Structures.
The sewer outfall, headwalls, manholes, gate boxes, or other structures shall be located so they do not interfere with the free discharge of flow through the stream.
D. Alignment. Sewer crossing streams should be designed to cross the stream as nearly perpendicular to the stream flow as possible and shall be free from change in grade. Sewer systems shall be designed to minimize the number of stream crossings.
(2) Construction.
A. Materials. Sewers entering or crossing streams shall be constructed of ductile iron pipe with mechanical joints; otherwise they shall be constructed so they will remain watertight and free from changes in alignment or grades. Material used to backfill the trench shall be stone, course aggregate, washed gravel, or other materials which will not readily erode, cause siltation, damage pipe during placement, or corrode the pipe.
B. Siltation and Erosion. Construction methods that will minimize siltation and erosion shall be employed. The design engineer shall include in the project specifications the method(s) to be employed in the construction of sewers in or near streams. Such methods shall provide adequate control of siltation and erosion by limiting unnecessary excavation, disturbing or uprooting trees and vegetation, dumping of soil or debris, or pumping silt-laden water into the stream. Specifications shall require that cleanup, grading, seeding, and planting or restoration of all work areas shall begin immediately. Exposed areas shall not remain unprotected for more than seven days.
(z) Sewage Pumping Stations.
(1) General.
A. When sewage pump stations are required, they shall be designed and installed per the following standards:
1. Great Lakes Upper Mississippi River Board (GLUMRB) (Ten States Standards) “Recommended Standards for Wastewater Facilities”, latest version.
2. OEPA’s latest requirements.
3. City of Urbana Design Criteria and Standard Construction Drawings.
4. All other applicable codes and regulations.
B. Flooding. The wastewater pumping station structures and electrical and mechanical equipment shall be protected from physical damage by the 100-year flood. Wastewater pumping stations should remain fully operational and accessible during the 25-year flood. Regulations of state and federal agencies regarding floodplain obstructions shall be followed.
(2) Pump station type and standard requirements. Listed below are the standard requirements for pump stations in the City. However, it is realized that certain situations may require other types of pump stations. It is highly recommended that early preliminary pumping station plans be submitted to the City for their approval prior to beginning final engineering.
A. Type. Submersible Pump Stations with separate wet well and valve chamber are preferred by the City.
B. Pump Type. Submersible explosion-proof pumps manufactured by Barnes Pumps Inc. capable of pumping raw, unscreened sewage, 3- inch spherical solids, and stringy materials typical of domestic sewage will be required. Multiple pumps shall be provided.
C. Electrical Installation.
1. All electrical installations and components shall be designed and installed per the National Electric Code (NEC) and all other electrical codes.
2. All equipment and components shall be housed in NEMA 4X stainless steel enclosures.
3. Controls and other equipment shall be Cutler-Hammer, or equivalent, as approved by the Engineer.
4. The cabinet shall be provided with a removable backplate on which all the components shall be mounted, with the exception of the H-O-A switches. The pump run lights shall be located on the outside door of the enclosure.
5. The pump control panel shall contain a circuit breaker, magnetic starter, hand-and-off-auto-selector-switch, run light, and seal leak indicating light for each pump.
6. There shall be furnished atop the control panel enclosure, a high-water alarm flashing red light.
D. Liquid level control. The pumps are to be controlled by four mercury float switches, with brackets fastened inside the wet well.
E. Alarm appurtenances.
1. Alarm signal shall be initiated by liquid level control system which shall be connected to a telemetering alarm system.
2. Power failure relay: Provide relay with N.O. contacts for hook up to a telephone line to be de-energized and contacts closed when power to station is interrupted.
3. High wet well level alarm: Provide high-water alarm for hook up to the telemetering system.
F. Guide system.
1. System design.
a. Permit removal of pumping units for inspection or service without dewatering wet well or interrupting operation of other pump equipment.
b. Pumps, when lowered into place, to be automatically connected to discharge piping with positive seal.
c. Incorporate fabricated aluminum access frame with provisions for mounting guide rails and hooks to retain pump cables.
2. Guide rails. Two lengths of stainless steel pipe with pilots; 2-inch Schedule 40, stainless steel (304) size per pump manufacturer’s recommendation. Top and bottom pilots shall be Class 30 cast iron with flake glass/polyester coating.
3. Pump guides.
a. Fabricated from bronze for spark proof operation.
b. Attached to pump volute with 316 stainless steel hex head cap screws.
4. Lift chain. Lift chain shall be 304 stainless steel, size to support pump with 4 to 1 safety factor.
G. Valve pit.
1. Valve pit structure (minimum 6-foot diameter) shall be constructed of pre-cast concrete sections conforming to ASTM C-478.
2. Valve pit access.
a. An aluminum access door and frame assembly shall be installed in the top slab. Minimum size shall be 36” x 36” unless larger is required by the City.
b. The door shall have a handle, latch in the open position, and have a hasp for a padlock. Surface shall be non-skid, diamond tread.
3. Valve pit drain. The valve pit floor shall be sloped to drain with a 3-inch drain pipe and check valve at the wet well as shown on the plans.
H. Wet well structure.
1. The wet well (minimum 6-foot diameter) shall be constructed of precast concrete sections conforming to ASTM C-478.
2. Wet well access. The door shall be of aluminum construction and have a handle, latch in the open position, and have a hasp for padlock. Surface shall be non-skid, diamond tread. Minimum size shall be 36” x 36” unless larger is required by the City.
3. Vent. A vent with screen shall be installed in the top slab.
4. Hoist stand. A hoist stand to fit existing pump hoist shall be mounted to the top slab to assure easy pump removal.
I. Piping and valves.
1. Materials. All piping and fittings beginning after the hydraulic sealing flange unit shall be 4-inch diameter ductile iron pipe with flanged joints. Pipe joints shall be flanged and conform with ANSI Specification A21.10 (AWWA C110) for cast iron pipe flanges and flanged fittings, Class 125.
2. Valves.
a. Check valves to be 4 inch with outside lever and weight. Valves to be rated for 175 psi water working pressure and 350 psi hydrostatic test pressure.
b. Eccentric plug valve to be 4 inch, specifically designed for sewage applications with 100% port opening. Valve to have cast iron with Buna-N rubber coating to minimize wear and corrosion. Seat rings to seal at 175 psi. Valves to have flanged ends (ANSI B16.1) and nut operator.
c. A guide disconnect assembly as shown on the plans shall be installed in the valve pit.
(aa) Force Mains.
(1) Velocity and diameter. At design pumping rates, a cleansing velocity of at least 2 feet per second should be maintained. The minimum force main diameter for raw wastewater shall be 4 inches.
(2) Air and vacuum relief valve. An air relief valve shall be placed at high points in the force main to prevent air locking. Vacuum relief valves may be necessary to relieve negative pressures on force mains. The force main configuration and head conditions should be evaluated as to the need for and placement of vacuum relief valves. Force mains shall be installed to keep high points and low points to a minimum.
(3) Termination. Force mains should enter the gravity sewer system at a point not more than 2 feet above the flow line of the receiving manhole.
(4) Pipe and design pressure. Pipe and joints shall be equal to water main strength material suitable for design conditions. The force main, reaction blocking, and station piping shall be designed to withstand water hammer pressures and associated cyclic reversal of stresses that are expected with the cycling of wastewater pump stations.
(5) Design friction losses. Friction losses through force mains shall be based on the Hazen and Williams formula or other acceptable methods. When the Hazen and Williams formula is used, the value of “C” shall be 100 for unlined iron or steel pipe for design. For other smooth pipe materials such as PVC, lined ductile iron, etc., a higher “C” value not to exceed 120 may be allowed for design.
(6) Identification. Where force mains are constructed of material which might cause the force main to be confused with potable water mains, the force main shall be appropriately identified.
(7) Leakage testing. Leakage tests shall be required per the water main testing requirements as shown in the City of Urbana Standard Construction Drawings.
(8) Cleaning of the force main. All force mains shall include sealed cleanouts for cleaning purposes at a maximum spacing of 600 feet or as approved by the City. (Ord. 4206. Passed 1-24-06.)